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•The advance of post-synthetic modification (PSM) of MOFs in the past five years was reviewed.•Two increasingly apparent tendencies in PSM of exploring new types and tandem reactions ...were demonstrated.•Selected examples including several from China focus on new types and tandem PSM.
In the past five years, post-synthetic modification (PSM) has become a very useful strategy in systematically functionalizing metal–organic frameworks (MOFs) by modifying the linker, metal node, pore character, and surface environment for the purpose of increasing the structural stability and introducing desired properties. In this review, we intend to demonstrate the two major trends in PSM including the mushrooming of new types of reaction and the combination of multi-steps PSM. The selected examples illustrate three promising PSM classes, post-synthetic metal exchange (PSME), post-synthetic ligand exchange (PSLE) and post-synthetic elimination and insertion (PSE&I). Combined with the well-developed covalent PSM and dative PSM, tandem PSM which constitutes of multistep and different types of reaction adds to the step-by-step improvement of catalytic activity, regulating magnetism and others. These recent advances in PSM not only open new paths to improve the function of MOFs, but also reveal the unprecedented reaction complexity of crystalline solids.
Abstract
Electrochromic (EC) materials with a dark-to-transmissive switch have great applications in optical communications, infrared wavelength detectors for spacecraft, and infrared camouflage ...coatings. However, such electroactive materials with high stability and cyclability are rare. Considering the advantages of the donor-acceptor approach (wide-range tuneable band position) and porous two-dimensional (2D) covalent organic framework (COF, well-ordered crystalline framework with stable structure and high surface area), in this work we constructed an extended delocalised π-electron layered dark purple EC-COF-1 by reacting the donor N,N,N′,N′-tetrakis(
p
-aminophenyl)-
p
-benzenediamine (TPBD) with the acceptor 2,1,3-benzothiadiazole-4,7-dicarboxaldehyde (BTDD). A sandwiched device made of EC-COF-1 exhibits the two-band bleaching (370 nm and 574 nm) in the visible region and becomes transparent under the applied potential with an induced absorption centring at 1400 nm. This discovery of a stable dark-to-transmissive switch in COF might open another door for their application in many EC devices for various purposes.
We present the syntheses, structural characterization, gas sorption, I2 uptake, and magnetic properties of a double-walled porous metal–organic framework, CoII 3(lac)2(pybz)2·3DMF (1·3DMF, purple, ...where pybz = 4-pyridyl benzoate, lac = d- and l-lactate) and of its post-synthetic modified (PSM) congeners, CoII 3(lac)2(pybz)2· xGuest (xGuest = 6MeOH, purple; 4.5EtOH, purple; 3PrOH, purple; 2C6H6, purple; 2.7I2, black), CoII 3(lac)2(pybz)2 (1, purple), CoII 3(pybz)2(lac)2(H2O)2·7H2O (1a·7H2O, green), and CoIIICoII 2(pybz)2(lac)2(H2O)2I·2H2O·1.5DMSO (1b·I– ·2H2O·1.5DMSO, yellow, DMSO = dimethyl sulfoxide). Crystallography shows that the framework is not altered by the replacement of DMF by different solvents or by the removal of the solvent molecules during the single-crystal to single-crystal (SC-SC) transformations, while upon exchange with H2O or partial oxidation by molecular iodine, the crystallinity is affected. 1 absorbs N2, H2, CH4, CH3OH, C2H5OH, PrOH, C6H6, and I2, but once it is in contact with H2O the absorption efficiency is drastically reduced. Upon PSM, the magnetism is transformed from a canted antiferromagnet (1·3DMF and 1·xGuest) to single-chain magnet (1), to a ferrimagnet (1a·7H2O), and to a ferromagnet (1b·I– ·2H2O·1.5DMSO). Raman spectroscopy suggests the color change (purple to green 1a·7H2O or yellow 1b·I– ·2H2O·1.5DMSO) is associated with a change of geometry from a strained octahedron due to the very acute chelating angle (∼60°) of the lactate of a cobalt center to a regular octahedron with a monodentate carboxylate and one H2O. The magnetic transformation is explained by the different interchain exchanges (J′), antiferromagnetic for 1·3DMF and 1·xSolvent (J′ < 0), SCM for 1 (J′ verge to 0), and ferromagnetic for 1a·7H2O (J′ > 0), between homometal topological ferrimagnetic chains (two octahedral and one tetrahedral CoII ions) connected by the double walls of pybz at 13.3 Å (shortest Co···Co). For 1b·I– ·2H2O·1.5DMSO the moment of the tetrahedral site is turned off, thus stabilizing a ferromagnetic state (J′ > 0). The present stabilization of four magnetic ground states is unique in the field of metal–organic frameworks as well as the electrical conductivity of 1·2.7I2.
To activate electronic and optical functions of the redox‐active metal–organic framework, (Me2NH2)InIII(TTFTB)⋅0.7 C2H5OH⋅DMF (Me2NH2@1, TTFTB=tetrathiafulvalene‐tetrabenzoate, ...DMF=N,N‐dimethylformamide), has been exchanged by tetrathiafulvalenium (TTF.+) and N,N′‐dimethyl‐4,4′‐bipyridinium (MV2+). These cations provide electron carriers and photosensitivity. The exchange retains the crystallinity allowing single‐crystal to single‐crystal post‐synthetic transformation to TTF@1 and MV@1. Both TTF.+ and MV2+ enhance the electrical conductivity by a factor of 102 and the visible light induced photocurrent by 4 and 28 times, respectively. EPR evidences synergetic effect involving charge transfer between the framework redox‐active TTFTB bridges and MV2+. The results demonstrate that functionalization of MOF by cation exchange without perturbing the crystallinity extends possibilities to achieve switchable materials.
By employing a single‐crystal‐to‐single‐crystal post‐synthetic transformation, electrical‐ and photo‐conductivity were activated by cation exchanges of dimethylammonium with tetrathiafulvalenium (TTF.+) and N,N′‐dimethyl‐4,4′‐bipyridinium (MV2+) into a redox‐active metal–organic framework containing TTF‐tetrabenzoate, (Me2NH2)InIII(TTFTB)⋅0.7 C2H5OH⋅DMF.
The structural transformations of metal nanoclusters are typically quite complex processes involving the formation and breakage of several bonds, and thus are challenging to study. Herein, we report ...a case where two lacunary Keggin polyoxometallate templated silver single-pods PW
O
@Ag
(SD/Ag51b) fuse to a double-pod (PW
O
)
@Ag
by reacting with 4,4'-bipyridine (bipy) or 1,4-bis(4-pyridinylmethyl)piperazine (pi-bipy). Their crystal structures reveal the formation of a 2D 4
-sql layer (SD/Ag72a) with bipy and a 3D pcu framework (SD/Ag72c) with pi-bipy. The PW
O
retains its structure during the cluster fusion and cluster-based network formation. Although the two processes, stripping of an Ag-ligands interface followed by fusion, and polymerization, are difficult to envisage, electrospray ionization mass spectrometry provides enough evidences for such a proposal to be made. Through this example, we expect the structural transformation to become a powerful method for synthesizing silver nanoclusters and their infinite networks, and to evolve from trial-and-error to rational.
An unusual high magnetic hardness for the layered perovskite-like (C2H5NH3)2FeIICl4, in addition to its already found canted antiferromagnetism, ferroelasticity, and ferroelectricity, which are ...absent for (CH3NH3)2FeIICl4, has been observed. The additional CH2 in the ethylammonium compared to methylammonium allows more degrees of freedom and therefore numerous phase transitions which have been characterized by single-crystal structure determinations from 383 to 10 K giving the sequence from tetragonal to orthorhombic to monoclinic (I4/mmm ↔ P42/ncm ↔ Pccn ↔ Pcab ↔ C2/c) accompanied by both tilting and rotation of the FeCl6 octahedra. The magnetic properties on single crystal and powder samples at high temperature are similar for both compounds, but at T N (C2H5NH3)2FeIICl4 is a proper canted antiferromagnet unlike the hidden canting observed for (CH3NH3)2FeIICl4. The canting angle is 0.6° toward the c-axis, and thus the moments lie in the easy plane of the iron-chloride layer defined by a critical exponent β = 0.18. The isothermal magnetizations for the field along the three orthogonal crystallographic axes show wider hysteresis for H ∥ c and is present at all temperature below 98 K. The coercive field increases as the temperature is lowered, and at T < 20 K it is difficult to reverse all the moments with the available 50 kOe of the SQUID for both single crystal and powder samples. The shape of the virgin magnetization after zero-field-cool (ZFC) indicates that the high coercive field is due to domain wall pinning. Thus, there are unusual associated anomalies such as asymmetric hysteresis and history dependence. The difference in magnetic hardness of the two compounds suggests that magnetic, electric, and elastic domains are intricately manifested and therefore raise the key question of how the different domains interact.
Abstract
High-nuclearity silver clusters are appealing synthetic targets for their remarkable structures, but most are isolated serendipitously. We report here six giant silver-thiolate clusters ...mediated by solvents, which not only dictate the formation of an octahedral Ag
6
4+
kernel, but also influence the in situ-generated Mo-based anion templates. The typical sevenfold symmetric silver nanowheels show a hierarchical cluster-in-cluster structure that comprises an outermost Ag
56
shell and an inner Ag
6
4+
kernel in the centre with seven MoO
4
2−
anion templates around it. Electrospray ionization mass spectrometry analyses reveal the underlying rule for the formation of such unique silver nanowheels. This work establishes a solvent–intervention approach to construct high-nuclearity silver clusters in which both the formation of octahedral Ag
6
4+
kernel and in situ generation of various Mo-based anion templates can be simultaneously controlled.
We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal–organic perovskite ABX3, C(NH2)3MII(HCOO)3, in which A=C(NH2)3 is guanidinium, B=M is ...a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO−. The compounds could be synthesized by either diffusion or hydrothermal methods from water or water‐rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna21. In the perovskite structures, the octahedrally coordinated metal ions are connected by the anti–anti formate bridges, thus forming the anionic NaCl‐type M(HCOO)3− frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn–Teller effect of Cu2+ results in a distorted anionic Cu–formate framework that can be regarded as Cu–formate chains through short basal CuO bonds linked by the long axial CuO bonds. These materials show higher thermal stability than other metal–organic perovskite series of AmineHM(HCOO)3 templated by the organic monoammonium cations (AmineH+) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin‐canted antiferromagnetism, with a Néel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6 K (Cu). In addition to the general spin‐canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin‐flop and a spin‐flip to the paramagnetic phase) within 50 kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics.
Nice cubes: A family of metal–organic perovskite salts of C(NH2)3M(HCOO)3 for divalent Mn to Zn were synthesized from water or water‐rich solutions. They possess anionic NaCl‐type frameworks of M(HCOO)3 with guanidinium in the cubic cavities (see figure); the magnetic members show spin‐canted antiferromagnetism.
Metal–organic frameworks (MOFs) incorporating lanthanide nodes and tetrathiafulvalene (TTF) linkers offer a viable approach for combining redox activity and magnetism in one material. Four rare-earth ...lanthanide ions (RE = Tb, Dy, Ho, and Er) were found to form isostructural MOFs consisting of metal chains bridged by redox-active tetrathiafulvalene-tetrabenzoate (TTFTB4–) whereby the carboxylate moieties act in both anti-anti and syn-syn coordination modes. These materials display tunable redox-active properties and slow magnetic relaxation phenomenon (Er and Dy). While the as-synthesized crystals contain the neutral diamagnetic TTF moiety, using either a solid-solution electrochemical method or iodine oxidation transforms part of the latter to the paramagnetic TTF•+ radical in a single-crystal-to-single-crystal manner without altering the internal structure of the building chains and the frameworks. This is accompanied by inclusion of I3 – replacing some of the solvents, as well as changes in the central C–C bond length of TTFTB, a strong EPR response at g ∼ 2, and an enhancement of the reflectance at low energies originating from absorption by the radical.
A highly stable pillared and double-walled zinc(II) metal-organic framework with regular nanochannels displays single-crystal to single-crystal transformation upon desolvation and a large quantity of ...iodine uptake, controlled release, and electrical conductivity elevation due to synergy between the iodine guests and the host framework.
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